php - Warning: mysqli_num_rows() expects parameter 1 to be mysqli_result, null given in -

i tried change mysql mysqli. , when error. tried found no solution this.

the error have: (what see not errors)

warning: mysqli_query() expects parameter 1 mysqli, null given in
c:\xampp\htdocs\follow\include\database.php on line 219

warning: mysqli_num_rows() expects parameter 1 mysqli_result, null given in c:\xampp\htdocs\follow\include\database.php on line 220

warning: mysqli_query() expects parameter 1 mysqli, null given in c:\xampp\htdocs\follow\include\database.php on line 231

warning: mysqli_num_rows() expects parameter 1 mysqli_result, null given in c:\xampp\htdocs\follow\include\database.php on line 232

warning: mysqli_query() expects parameter 1 mysqli, null given in c:\xampp\htdocs\follow\include\database.php on line 102

... more errors

and php code

<?php /**  * please subscribe our feeds @ http://blog.geotitles.com more such tutorials  */ include("constants.php"); class mysqldb   {   var $connection;         //the mysql database connection  var $num_active_users;   //number of active users viewing site  var $num_active_guests;  //number of active guests viewing site  var $num_members;        //number of signed-up users  /* note: call getnummembers() access $num_members! */     /* class constructor */   function mysqldb(){   /* make connection database */   $con = mysqli_connect(db_server, db_user, db_pass,db_name);    // check connection  if (mysqli_connect_errno())      {    echo "failed connect mysql: " . mysqli_connect_error();     }        /**      * query database find out number of members     * when getnummembers() called first time,     * until then, default value set.     */     $this->num_members = -1;      if(track_visitors){      /* calculate number of users @ site */      $this->calcnumactiveusers();       /* calculate number of guests @ site */      $this->calcnumactiveguests();     }    }      function confirmuserpass($username, $password){    global $con;    /* add slashes if necessary (for query) */   if(!get_magic_quotes_gpc()) {       $username = addslashes($username);    }     /* verify user in database */    $q = "select password ".tbl_users." username = '$username'";    $result = mysqli_query($con,$q);    if(!$result || (mysqli_num_rows($result) < 1)){      return 1; //indicates username failure    }     /* retrieve password result, strip slashes */    $dbarray = mysqli_fetch_array($result);    $dbarray['password'] = stripslashes($dbarray['password']);    $password = stripslashes($password);    /* validate password correct */   if($password == $dbarray['password']){      return 0; //success! username , password confirmed    }    else{      return 2; //indicates password failure   }   }       function confirmuserid($username, $userid){    global $con;   /* add slashes if necessary (for query) */   if(!get_magic_quotes_gpc()) {       $username = addslashes($username);   }    /* verify user in database */   $q = "select userid ".tbl_users." username = '$username'";   $result = mysqli_query($con,$q);   if(!$result || (mysqli_num_rows($result) < 1)){      return 1; //indicates username failure    }    /* retrieve userid result, strip slashes */   $dbarray = mysqli_fetch_array($result);   $dbarray['userid'] = stripslashes($dbarray['userid']);   $userid = stripslashes($userid);    /* validate userid correct */   if($userid == $dbarray['userid']){      return 0; //success! username , userid confirmed   }   else{      return 2; //indicates userid invalid   }   }     function usernametaken($username){    global $con;     if(!get_magic_quotes_gpc()){      $username = addslashes($username);    }   $q = "select username ".tbl_users." username = '$username'";   $result = mysqli_query($con,$q);   return (mysqli_numrows($result) > 0);   }    function usernamebanned($username){   global $con;   if(!get_magic_quotes_gpc()){      $username = addslashes($username);   }   $q = "select username ".tbl_banned_users." username = '$username'";   $result = mysqli_query($con,$q);   return (mysqli_numrows($result) > 0);   }  function addnewuser($username, $password, $email){ global $con;   $time = time();   /* if admin sign up, give admin user level */   if(strcasecmp($username, admin_name) == 0){      $ulevel = admin_level;   }else{      $ulevel = user_level;   }   $q = "insert ".tbl_users." values ('$username', '$password', '0', $ulevel,     '$email', $time)";   return mysqli_query($con,$q);   }    function updateuserfield($username, $field, $value){   $q = "update ".tbl_users." set ".$field." = '$value' username = '$username'";   return mysqli_query($con,$q); }      function getuserinfo($username){  global $con;   $q = "select * ".tbl_users." username = '$username'";   $result = mysqli_query($con,$q);   /* error occurred, return given name default */   if(!$result || (mysqli_num_rows($result) < 1)){      return null;   }   /* return result array */   $dbarray = mysqli_fetch_array($result);   return $dbarray;   }    function getnummembers(){  global $con;   if($this->num_members < 0){      $q = "select * ".tbl_users;      $result = mysqli_query($con,$q);      $this->num_members = mysqli_num_rows($result);    }   return $this->num_members;   }      /**    * calcnumactiveusers - finds out how many active users    * viewing site , sets class variable accordingly.    */    function calcnumactiveusers(){  global $con;   /* calculate number of users @ site */   $result = mysqli_query($con,"select * ".tbl_active_users);   $this->num_active_users = mysqli_num_rows($result);      }     function calcnumactiveguests(){     global $con;   /* calculate number of guests @ site */   $q = "select * ".tbl_active_guests;   $result = mysqli_query($con,$q);   $this->num_active_guests = mysqli_num_rows($result);    }      function addactiveuser($username, $time){  global $con;   $q = "update ".tbl_users." set timestamp = '$time' username = '$username'";   mysqli_query($con,$q);    if(!track_visitors) return;   $q = "replace ".tbl_active_users." values ('$username', '$time')";   mysqli_query($con,$q);   $this->calcnumactiveusers();    }   function addactiveguest($ip, $time){  global $con;   if(!track_visitors) return;   $q = "replace ".tbl_active_guests." values ('$ip', '$time')";   mysqli_query($con,$q);   $this->calcnumactiveguests();    }   function removeactiveuser($username){  global $con;   if(!track_visitors) return;   $q = "delete ".tbl_active_users." username = '$username'";   mysqli_query($con,$q);   $this->calcnumactiveusers();    }  /* removeactiveguest */ function removeactiveguest($ip){ global $con;   if(!track_visitors) return;   $q = "delete ".tbl_active_guests." ip = '$ip'";   mysqli_query($con,$q);   $this->calcnumactiveguests(); }  /* removeinactiveusers */ function removeinactiveusers(){ global $con;   if(!track_visitors) return;   $timeout = time()-user_timeout*60;   $q = "delete ".tbl_active_users." timestamp < $timeout";   mysqli_query($con,$q);   $this->calcnumactiveusers(); }  /* removeinactiveguests */ function removeinactiveguests(){  global $con;   if(!track_visitors) return;   $timeout = time()-guest_timeout*60;   $q = "delete ".tbl_active_guests." timestamp < $timeout";   mysqli_query($con,$q);   $this->calcnumactiveguests(); }   function query($query){ global $con;   return mysqli_query($con,$query); } };     $database = new mysqldb;    ?> 

the error vague, specific. it's stating connection object, mysql_result, expected it's receiving null instead.

the reason how you're attempting use connection inside each function:

global $con; mysqli_query($con, $q); 

the global keyword will bring in global variables function you're using in, $con isn't global variable in class (and, don't need use global inside classes). you're looking instead $this keyword.

in class constructor mysqldb() define $con variable; should instead change use $this->connection you've defined global variable named $connection:

$this->connection = mysqli_connect(db_server, db_user, db_pass,db_name); 

then, in each function, instead of using like:

global $con; mysqli_query($con,$q); 

you can use:

mysqli_query($this->connection, $q);